The present invention relates generally to rotor structures for dynamoelectric machines and, more particularly, to rotor structures which include means to preserve the installation integrity of a resin coating as normally employed on such structures.
It is well known in the dynamoelectric machine discipline to provide a rotor structure which, after assembly of the basic mechanical part, is provided with an insulating coating, normally of a resinous nature (often referred to as varnish) over all of the structure except for the bearing surfaces; e.g., shaft bearing surfaces and, where applicable, a commutator or slip rings. In certain large machines, in addition to the main rotor windings, there are included equalizer windings connected to the main windings to equalize the currents in the main windings. Whereas the main windings are supported by a magnetic structure (for example, laminations) the equalizer windings are often encapsulated in an insulating material, such as an epoxy, to form an assembly of an annular configuration. Since the equalizer windings do not have a magnetic supporting structure as such, there is often employed a metallic winding support member, supported by the shaft, around which the annular equalizer winding assembly is disposed.
The circular joint or interface between the encapsulated annular equalizer winding assembly and the winding support member can present a problem to the insulating integrity of the resin coating. First of all, the epoxy of the equalizer winding configuration normally will have a different temperature coefficient of expansion than the metallic winding support member. Compounding this difference is the fact the equalizer windings themselves are an array of current carrying members arranged in an annulus around the winding support and solidly connected by leads to the main windings and thus represent a heat source, resulting in a concentration of heat in the epoxy with respect to the winding support. Further, current heating in the main windings causes those windings to expand in the direction of their length (axially). Since the equalizer windings are solidly connected by leads to the main windings, the equalizer winding assembly also moves axially with the main windings to cause a separation between the encapsulated equalizer winding and the winding support at the interface thereof. Since the resinous (varnish) coating tends to be somewhat inflexible, resultant stresses can result in cracks in the resin coating at the interface between the annular equalizer winding assembly and the winding support member. This crack, or cracks, creates a collection area for dirt, grease, etc., and in machines having carbon brushes, dust resulting from brush wear. This contamination reduces the insulating integrity of the coating and is a potential problem area in that it increases the possibility of arcing between the various windings and the basic metallic structure of the machine.